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United States Patent | 5,352,887 |
Morgan ,   et al. | October 4, 1994 |
A circuit for detecting a substance in motion. A light source (11) emits light which is received by a first photodetector (16) and a second photodetector (18). Each of the photodetectors (16) and (18) receives substantially equal light intensities from the light source (11). The first photodetector (16) generates a first output voltage (17) which corresponds to light intensity. The second photodetector (18) generates a second output voltage (19) which corresponds to light intensity. A differential amplifier (21) has a first input coupled to the first output voltage (17) and a second input coupled to the second output voltage (19). A moving substance (13) passing between the light source (11) and the first (16) or second (18) photodetectors generates a differential voltage which is amplified by the differential amplifier (21).
Inventors: | Morgan; Damon (Phoenix, AZ); Gempe; Horst (Phoenix, AZ) |
Assignee: | Motorola, Inc. (Schaumburg, IL) |
Appl. No.: | 171990 |
Filed: | December 23, 1993 |
Current U.S. Class: | 250/222.1; 250/208.2; 250/577; 347/19 |
Intern'l Class: | G01V 009/04 |
Field of Search: | 250/221,222.1,222.2,223 R,561,208.2,577 356/335,28 |
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